A decorative material prepared by gravure printing has so far been given a decoration comprising a gravure ink. The gravure ink has been composed of color pigments, including a red pigment of the monoazo type, a yellow pigment of the bisazo type, copper phthalocyanine blue, and carbon black; and a binder for the pigments, such as a rosin derivative or a linear polyester.
Except for copper phthalocyanine blue and carbon black, however, these materials were poor in light fastness (especially weather resistance). When exposed to sunlight for a long time, therefore, an ordinary ink for architectural materials, used as a source of a mixture of primary colors, yellow, red, blue and black, undergoes fading of the red and yellow in the ink, thereby discoloring the inked decorative material into a blue or black tone. When such an ordinary ink for architectural materials, as a source of a mixture of primary colors, yellow, red, blue and black, is applied to a surface of mortar or the like from which an alkaline component seeps, the red and yellow fade, producing a decoration with a bluish black tone. Besides, the binder is attacked, whereby the decoration may fall off.
It was easy to select pigments, thereby improving weather resistance alone, or alkali resistance alone. However, it was difficult to find a red pigment and a yellow pigment that possess both of these properties. For example, a red pigment comprising quinacridone and a yellow pigment comprising isoindolinone were very high in weather resistance, but insufficient in alkali resistance. Red and yellow pigments of the polyazo type were excellent in alkali resistance, but insufficient in weather resistance.
To prevent deterioration of the decoration, it has been practiced to incorporate an ultraviolet absorber into its topcoat layer and apply several coatings of an acrylic paint having light fastness, or to provide the mortar surface with a primer layer having alkali resistance in order to prevent the seepage of the alkaline component.
These methods, however, require a topcoat or a primer which are expensive, special materials. They also pose the problem of increasing the number of steps and the expenses, because surplus layer formation is involved. Furthermore, even when the topcoat layer is light fast, the pigments as colorants, if poor in light fastness and alkali resistance, fade and discolor the entire decoration in a bluish black look.
By using copper phthalocyanine blue as a blue pigment and carbon black as a black pigment, it is possible to make an ink satisfactory in both weather resistance and alkali resistance. However, there may be a desire to employ other kinds of pigments because of the price, tone, and required properties before than weather resistance and alkali resistance. This desire cannot be satisfied by the use of copper phthalocyanine blue and carbon black. For blue and black as well, there has been need to increase the variety of feasible pigments.